Bruce Rymer

Acoustical Absorption of Porous Pavement

Acoustical absorption coefficients of more than 140 pavement cores were obtained by the impedance tube method with two microphones and cross-spectral analyses. The effectiveness of the impedance tube in predicting noise reduction for different mixes was evaluated by comparing the correlations between onboard sound intensity levels and absorption. Theoretical predictions of acoustical absorption due to friction between air and porous matrix and thermal relaxation were compared with measured results for an idealized porous structure. The model was used to infer porosity, tortuosity, and pore size from measured acoustical absorption spectra for manufactured porous asphalt and extrapolate test results to nonnormal angles of incidence, assuming isotropy of the porous structure. This model will help improve mix designs to increase the absorption of pavement surfaces and can be used to estimate porous pavement properties.

Comparison of tire-pavement noise characteristics of rubberized and conventional asphalt concrete mixes

This study compares tire/pavement noise characteristics of flexible pavement sections in California using the On-Board Sound Intensity (OBSI) method. Two experiments are presented in this work. The first one compares noise properties of pavement sections of different ages constructed with open-graded rubberized asphalt concrete (RAC-O) and gap-graded rubberized asphalt concrete (RAC-G) versus sections with conventional open-graded asphalt concrete (OGAC) and dense-graded asphalt concrete (DGAC). The second experiment compares the performance of trial sections that used different modified rubberized asphalt mixes as surface course. The results show that, compared with conventional asphalt concrete surface course of the same age, rubberized asphalt concrete surface courses have lower tire-pavement noise levels. The reduction comes mainly from better durability of rubberized asphalt concrete mixes. Additional information analyzed in this quieter pavement research study includes the effect of mix design variables and pavement surface distresses on tire-pavement noise characteristics of rubberized and conventional asphalt concrete mixes.

California-Denmark Study on Acoustic Aging of Road Pavements

Knowledge of acoustic aging of road pavements is needed by road administrators when developing policies and strategies for noise abatement. It is important to know how noise-reducing pavements, as well as pavements without such acoustic properties, perform over time. Methods such as the American traffic noise model method or the Nordic NORD2000 method use acoustic aging for accuracy in predicting noise. Noise performance models for road pavements are necessary if noise is to be integrated as an active parameter in pavement management systems. This paper contributes to ongoing international development in the field of acoustic aging by performing a comprehensive analysis of results from four Californian and Danish long-time noise measurement studies on asphalt pavements. There is not much information on which changes in the surface structure cause an increase in noise in the period between when the bitumen film is worn off and when the pavement begins to deteriorate with distresses such as raveling, cracking, and so forth. This study analyzes and compares trends in the development of noise over time. The development of the noise spectra is also analyzed. The increase of noise has normally been analyzed in relation to the age of pavements. The traffic load and an artificial indicator, defined as the change of noise predicted as a combination of actual physical age and traffic load, are investigated.

Effects of Aging on Tire-Pavement Noise Generation for Concrete Pavements of Different Textures

Between 2003 and 2010, research on the changes in tire–pavement noise generation over time was conducted on 11 textures applied to portland cement concrete. The initial textures included longitudinal tining, burlap drag, and longitudinal broom. Additional texturing was applied to these surfaces in the form of longitudinal grooving of varying depth and spacing and diamond grinding with varying spacer dimensions, as well as a combination of the two. Since their application, these sections have been routinely monitored for tire noise performance with the onboard sound intensity method. As originally measured in June 2003, the range in level between the surfaces was relatively small at 2.7 dB. At 5 years, the range is slightly smaller at 2.3 dB. During the total 71/2 years of the study, the overall noise performance increased at an average rate of about 0.10 dB per year. The study has shown that for different frequency ranges the change in noise level has displayed some variation; the lower-frequency levels have decreased for some pavements with time, while the higher-frequency levels have increased at a rate higher than the overall levels for all pavements. For the higher frequencies, findings suggested that the increased noise was due to polishing of the surfaces. For the lower frequencies, the reduction in noise level was less pronounced with more variability between textures. For the ground surfaces, some evidence was found that indicated that the reduction might be linked to some loss of larger-scale texture as the surfaces were worn down.

Determining End Limits of Quieter Pavement Projects

Ongoing work in the area of tire pavement–acoustics has definitively determined that there can be a significant variation of noise levels between the loudest and quietest pavements. With the use of the onboard sound intensity (OBSI) measurement procedure, it has also been determined that tire–pavement noise is highly correlated to the overall traffic noise levels, especially when traffic is flowing at freeway speeds. OBSI presents road agencies with a potential new tool for lowering traffic noise levels by using quieter pavements. Changing from a loud or old and raveled pavement to a newer, smoother, lower noise pavement can yield acoustic benefits to roadside communities or “receivers.” The decrease in noise level depends on the difference between OBSI levels of the existing pavement and the selected quieter pavement, and the magnitude of this decrease may also be influenced by vehicle mix. After the decision to use a quieter pavement has been made, the end limits for the pavement must be determined. The problem is somewhat similar to deciding where to terminate a sound wall relative to the location of the roadside receivers. This analysis determined that the quiet pavement end limits were less sensitive to variation in typical roadway cross sections, somewhat sensitive to the distance between the receiver and the roadway and where the quiet pavement terminates, and very sensitive to the absolute differences between the noisier and quieter pavements.

Measurement of Vertical Distribution of Truck Noise Sources During Highway Cruise Pass-Bys by Acoustic Beam Forming

A measurement program was completed to determine the vertical distribution of heavy-truck noise sources for pass-by events on an in-service highway for vehicles operating under cruise conditions. In addition to data on heavy trucks, some data were obtained for medium trucks and light-duty vehicles. The measurements were performed with acoustic beam forming, which provided visualization of the sound radiation of passing vehicles as well as means for calculating the vertical distribution of noise source level. The data set includes pass-by events for 125 heavy trucks, 30 medium trucks, and nine light vehicles operating nominally at 55 mph on two asphalt surfaces. The purposes of the research were to compare the source height splits assumed in the FHWA traffic noise model (TNM) to the results of this work, examine the acoustic benefit of sound walls designed to block the line of site of truck exhaust outlets, and obtain a better understanding of truck noise sources. For heavy trucks, the pass-by noise is dominated by tire noise produced by the drive axles, with other secondary sources related to the power train occurring in some cases. Noise from elevated exhaust outlets was not observed except in one or two special cases. For all vehicle types, ground level sources (tire noise) produced the highest noise levels. Furthermore, the vertical source distributions were found to be virtually identical for heavy and medium trucks. For truck and light vehicles, it appeared that the current source height splits assumed in TNM may be biased toward higher upper-source strength.

Community reaction to noise from a replaced bridge span and associated approach

A newly constructed replacement of the westbound span of the Carquinez Bridge on Interstate I‐80 in the San Francisco Bay Area was recently opened for service. Although the traffic volume and mix remained the same as it was before the project, there was a very strong reaction to the noise produced by the new construction from nearby residences. For these residences, the predicted noise levels were only expected to increase by less than 2 dB due to the bridge and its approaches being somewhat closer to the community. The complaints had two aspects: generally higher traffic noise levels and impulsive slaps from the expansion joints in the viaduct connecting the bridge deck to the at‐grade roadway. Although clearly audible in the community, the joint slaps did not contribute to any of the common community traffic noise metrics. For noise mitigation, the viaduct surface was ground to reduce overall tire/pavement noise, however, there was concern that by reducing the masking effect of the pavement texture gene...